International Patent Application No. 94/18041 describes a method and a circuit arrangement for determining the force exerted on the pedal as a controlled variable for a braking system equipped with anti-lock control. The braking system includes, inter alia, a hydraulic pump. The hydraulic pump is used to recirculate pressurized media that had been drawn from the wheel brake to reduce pressure. On the other hand, the hydraulic pump is used to supply auxiliary pressure. In the method described in International Patent Application No. 94/18041, during a closed-loop control braking, the drive motor of a hydraulic pump is switched over to generator operation, and the level of the generator voltage and its decay behavior are evaluated. From the generator voltage and the decay behavior, one is able to determine by approximation the initial pressure that is a function of the force exerted on the pedal.
German Patent Application No. 38 19 490 A1 describes a pump system of a hydraulic final controlling element for adjusting a movable member of an object. This object is, for example, a brake of an anti-lock control system of a motor vehicle. The pump system has an electromotor for driving a pump, which is used to exert influence on a hydraulic fluid pressure. In addition, the pump system comprises a testing device for determining the pressure of the hydraulic fluid and, thus, for monitoring the performance reliability of the hydraulic. In this context, the pressure is not measured with the aid of a sensor, but rather using as a baseline the detected engine speed, the detected active current consumption of the electromotor, and the active operating voltage at the electromotor. Using as a baseline the determined pressure value of the hydraulic fluid, the electromotor is driven, i.e., the performance reliability of the hydraulic is monitored. In addition, German Patent Application No. 38 19 490 A1 describes a method of determining the torque of the electromotor using the motor voltage and the motor current as a baseline.